The present invention relates to spray guns and in particular, relates to compressed air operated spray guns for applying plaster and other particulate material.
Handheld spray guns for applying plaster and other particulate matter are well known. One particular spray gun which is proven acceptable in the field, is disclosed in our U.S. Pat. No. 4,502,640. This spray gun is easy to control and is not prone to plugging or jamming. Although the gun works well, it is somewhat time consuming to disassemble and clean. In addition there is no adjustment to hold the trigger in an operating position for spraying at a fixed rate which is suitable for large continuous applications. It is desirable to provide a spray gun which is easier to clean and can be disassembled and reassembled in a fast, efficient manner.
A spray gun for spraying of plaster and other particulate material comprises a barrel portion having a chamber for containing material to be sprayed, an entrance into the chamber for receiving the material to be sprayed, a slidable tube for providing a source of compressed air to the chamber and extending out of one end of the barrel portion, and a nozzle plate at the end of the barrel and selectively closable by the slidable tube. The slidable tube includes a spring bias member which is engaged by said slidable tube and is compressed by movement of the slideable tube away from the nozzle plate and provides a bias to close the nozzle. A handle portion of the gun extends downwardly from one end of the barrel and contains a slidable trigger mechanism. The slidable trigger mechanism includes a finger grip fixed on a shaft which is generally parallel to the slidable tube. The shaft of the slidable trigger mechanism includes a connecting link member at an end of the shaft opposite the finger grip. The link member is slidable on the slidable tube and trapped between an adjustable stop member on the slidable tube and a further member secured on the slidable tube. The trigger mechanism, when the finger grip is moved towards the handle portion, forces the link member to engage the further member and move the slidable tube away from the nozzle plate against the spring bias. Release of the finger grip allows the spring bias in combination with the adjustable stop to return the slidable tube to the closed position and in so doing, return the trigger mechanism to the closed position.
According to an aspect of the invention, the adjustable stop member is movable along the slidable tube to hold the slidable tube in an open position without actuation of the trigger mechanism.
In yet a further aspect of the invention, the slidable tube has a threaded portion at one end thereof and the adjustable stop member is threaded on the threaded portion. The biased slidable tube causes the adjustable stop member and the link member to return to an initial position when the trigger is released.
According to yet a further aspect of the invention, the handle portion includes an adjustable stop between the handle portion and the trigger to adjustably limit the extent the finger grip can move towards the handle portion. This allows the user to limit the maximum movement of the trigger and thereby define a maximum open position for a particular job.
In yet a further aspect of the invention, the adjustable stop member on the threaded portion of the slidable tube is adjustable to define different fully open positions of the slidable tube.
In yet a further aspect of the invention, the threaded portion of the slidable tube receives a control valve for adjusting the supply of compressed air through the slidable tube to the chamber of the barrel portion.
In yet a further aspect of the invention, the control valve has an extended threaded port for engagement with the threaded tube in various positions of the adjustable stop and forms a nut lock relationship therewith to maintain a particular position of the adjustable stop.
In yet a further aspect of the invention, the control valve is a fast shut off valve.
In yet a further aspect of the invention, the barrel portion includes a threaded port and an end opposite the nozzle plate which is closed by a threaded bearing which slidably supports the slidable tube.